The present invention relates to metal-sulfur type cells for making secondary batteries, and particularly to cells operating with all components thereof in the solid state.
Secondary batteries are in widespread use in modern society, particularly in applications where large amounts of energy are not required. However, it is desirable to use batteries in applications requiring considerable power, and much effort has been expended in developing batteries suitable for such high power applications as electric vehicles. Of course, such batteries are also suitable for use in lower power applications such as cameras or portable recording devices.
At this time, the most common secondary batteries are probably the lead-acid batteries used in automobiles. These batteries have the advantage of being capable of operating for many charge cycles without any significant loss of performance. However, these batteries have a low power to weight ratio. In order to improve on weight ratios, lithium batteries have been thoroughly investigated, and certain of these systems are promising in certain applications. As improvements are made, it will be appreciated that more widespread use will follow.
Developments in lithium polyethylene oxide cells typically have a figure of merit (FOM), which is computed by multiplying the number of cycles by the mean cycle capacity and dividing by the excess installed lithium capacity, of about 50. A typical example of such a cell is to be found in U.S. Pat. No. 4,589,197 describing a lithium/polyethylene battery system in which the electroactive material is an intercalation compound. This type of battery has also been shown to be capable of scaling up to large sizes without any significant loss of performance.
Another lithium type cell is to be found in U.S. Pat. No. 4,833,048 which utilizes an organsulfur positive electrode which has sulfur-sulfur bonds in the charged state that are broken in the discharged state to form organometal salts. This patent discloses a cell which has an excellent weight ratio, however, the disclosed electrode was utilized in the liquid state and solvents were needed to provide the desired current transport. The present invention provides improvements over these patented systems. Specifically, the present invention provides a cell having a FOM of the order of 120 along with capability of operation at room or ambient temperatures.